The present invention relates to a photosensitive material for electrophotography. More particularly, it relates to a photosensitive material for electrophotography which has a high photosensitivity to rays having a wavelength included in the oscillation wavelength region of a laser printer, especially a semiconductor laser printer, and also which has a high charge potential.
Many photosensitive materials, such as Se, Se-Te, CdS, ZnO, and organic photoconductors, are known as photosensitive materials having a sensitivity to rays having a wavelength included in the visible ray wavelength region, that is, the wavelength region of from 370 to 720 nm. Some of these photosensitive materials have already been used in practice for electrophotographic copying machines or laser printers comprising an He-Ne laser as the beam source. However, almost no photosensitive materials have been known having a sensitivity to rays having a wavelength included in the semiconductor laser oscillation wavelength region, that is, the near infrared ray wavelength region. Only CdS, As-Te-Se, and phthalocyanine photosensitive materials are known.
CdS and As-Te-Se photosensitive materials are harmful and poisonous. Use of these photosensitive materials is undesirable because of environmental pollution and also because of the necessity for special consideration to safety in the manufacturing process. As-Te-Se photosensitive material is further disadvantageous as its manufacturing process requires a vacuum evaporation deposition apparatus and is complicated. And, while CdS has good photosensitivity, it is disadvantageous in that it requires a special charging process since the charge acceptance is low.
Phthalocyanine pigment, on the other hand, has long been known to have photoconductivity, is cheap, and is very low in toxicity. Research has consequently been performed on applications of phthalocyanine pigment in the field of electrophotography to copying machines, laser printers, and the like as the photosensitive material. Phthalocyanine pigment cannot be used for the production of a photosensitive material alone because it has no film-forming property and because vacuum evaporation deposition thereof is very difficult. Accordingly, a photoconductive film is ordinarily formed by dissolving or dispersing the phthalocyanine pigment together with a binder in an organic solvent. The thus formed photoconductive coating solution or dispersion is then coated at a dried thickness of several microns to scores of microns on an electroconductive substrate by means of a doctor blade, a bar coater, a roll coater, or the like.
The photosensitive film of the phthalocyanine pigment prepared according to the above-mentioned process shows a so-called induction phenomenon in which the decay just after irradiation is very small, that is, the irradiation energy is not utilized at a high efficiency. Accordingly, this photosensitive film is not sufficiently sensitive for the photosensitive material for a copying machine for electrophotography or a laser printer. The sensitivity to rays having a wavelength included in the semiconductor laser oscillation wavelength region is especially low.
As a means for overcoming the foregoing difficulties involved in the phthalocyanine photosensitive material, the present inventors have already proposed the addition of an oxadiazole derivative and of tetrathiafulvalene as third components to the phthalocyanine photosensitive material (Japanese Patent Application Nos. 55-120767 and 55-120779, respectively). However, the photosensitivity and charging property of these proposed photosensitive materials are still insufficient for photosensitive material for semiconductor laser printers.
Under these circumstances, the present inventors made various examinations on the above-mentioned phthalocyanine photosensitive material. As a result, the present inventors found that a photosensitive material for electrophotography which comprises a phthalocyanine pigment, poly-N-vinylcarbazole (PVCz), and an organic resin in which said phthalocyanine pigment and poly-N-vinylcarbazole are dispersed, wherein the weight ratio of phthalocyanine to PVCz is in the range of from 1.2 to 12 and the content of the organic resin is 35% to 70% by weight based on the total amount of the photosensitive material, possesses excellent photosensitivity and a high charge potential. On the basis of these findings, the present inventors accomplished this invention.
Prior patent applications with the same object as the present invention and disclosing a composition of the photosensitive material partially similar to the photosensitive material of the present invention include Japanese Laid-Open Patent Application No. 53-9537 (Toyo Ink K.K.) and Japanese Patent Application Publication No. 56-17657: (Xerox corporation). Japanese Laid-Open Patent Application No. 53-9537 relates to a method for sensitizing a poly-N-vinylcarbazole type photosensitive material for electrophotography, characterized in that 0.01 to 10 parts by weight of a phthalocyanine photoconductor, e.g. copper phthalocyanine, per 100 parts by weight of a polyvinylcarbazole type photoconductor, e.g., poly-N-vinylcarbazole, are dispersed in a binder resin. In this case, the weight ratio of copper phthalocyanine to PVCz is in the range of from 0.0001 to 0.1, which range is quite different from that in the present invention. This difference is considered to be ascribable to the following reasons. In Japanese Laid-Open Patent Application No. 53-9537, copper phthalocyanine, which is used as a sensitizer, is used for widening the spectral response of PVCz. The above-mentioned range is adopted for the purpose of maintaining the retention of charge, transparency, and self-film-forming property of the photosensitive material at satisfactory levels. On the other hand, in the present invention, copper phthalocyanine is mainly used for enhancing the photoconductivity of the photosensitive material. PVCz plays only an auxiliary role in the enhancement of the photosensitivity. As a result, the above-mentioned range is adopted. Also, PVCz and the organic resin contribute to the retention of charge of the photosensitive material.
Japanese Laid-Open Patent Application No. 53-9537 further discloses a styrene-acryl copolymer as the binder resin. The amount of this copolymer that is used is about 8.7% by weight based on the total amount of the photosensitive material, which amount is also different from the amount of the organic resin used in the present invention.
Japanese Patent Application Publication No. 56-17657 discloses an electron radiation-sensitive material comprising a phthalocyanine photoconductor and a PVCz photoconductor. In this case, an X-type metal-free phthalocyanine is used as the phthalocyanine photoconductor. The weight ratio of phthalocyanine to PVCz is in the range of from 0.00125 to 0.0625, which range is different from that in the present invention. The above-mentioned range disclosed in this patent is selected for obtaining an optimal mechanical property of the photosensitive material. Also, this patent only exemplifies various organic resins as the binder, and neither discloses nor suggests the amount of these resins used.